As is known, ski boots for ski mountaineering currently on the market basically comprise: a rigid shell made of plastic or composite material, which is shaped so as to accommodate the foot of the user, and has the lower part specifically structured so as to be fixed to the back of a downhill ski or similar by means of a special ski binding device; a rigid cuff made of plastic or composite material, which is shaped so as to embrace the lower part of the leg of the user from the behind, and is hinged to the upper part of the shell so as to be able to rotate about a transversal reference axis which is substantially perpendicular to the vertical midplane of the boot, and is also locally substantially coincident with the articulation axis of the ankle; an upper oblong tongue usually made of plastic material, which is arranged resting on the upper part of the shell, outside of the shell, so as to cover the longitudinal slit which extends straddling the midplane of the boot, in the area of the shell above the instep; and an inner liner in soft, thermal-insulating material, which is inserted inside the shell and the cuff, and is shaped so as to receive and protect both the foot and the lower part of the user's leg.
In addition the above-mentioned ski boots comprise a shell closing mechanism and a cuff closing mechanism, both manually operated.
In the more sophisticated models, the shell closing mechanism usually comprises: a manually-operated cable-winding winch which is rigidly fixed on the upper side of the tongue with the winch rotation axis locally substantially perpendicular to the surface of the tongue; a number of fairlead elements which are attached rigidly to the shell, on opposite sides of the longitudinal slit of the latter; and lastly a flexible cable made of metal material, which comes out of the cable-winding winch, slidingly engages in succession the various fairlead elements present on the shell passing alternately from one side of the shell longitudinal slit to the other above the tongue, and lastly returns back inside the cable-winding winch.
Despite working excellently, experimental tests have shown that, when used in conjunction with a shell composed of one or more overlapping layers of carbon fibres embedded in the resin, the above-described winch lacing system has a very limited capability to tighten the shell onto the foot of the user so that the shape of the composite-material shell must be almost tailor-made for the user, with all the drawbacks that this entails.
To better meet the market demands, the manufacturer of ski mountaineering boots must produce the composite-material shells in a larger number of sizes, with the increased costs that this entails.